Engineering tools · Free to use
Reynolds Number Calculator
Calculate Reynolds number from fluid properties, speed and hydraulic diameter.
Input parameters
Inputs and calculations stay in this browser.
Result
Dimensionless result; for a non-circular duct hydraulic diameter is normally four times the flow area divided by wetted perimeter.
Equation
Re = ρ v Dh / μ
Applicability
Use properties at the relevant fluid state. Speed must be non-negative; density, diameter and dynamic viscosity must be positive. Transition criteria depend on geometry and flow conditions.
Notes
Dimensionless result; for a non-circular duct hydraulic diameter is normally four times the flow area divided by wetted perimeter.
Worked example
For a single fluid state, using density ρ = 1000 kg/m³, speed v = 2 m/s, hydraulic diameter Dh = 0.05 m and dynamic viscosity μ = 0.001 Pa·s gives Re = 1000 × 2 × 0.05 / 0.001 = 100000 (dimensionless). These properties and dimensions are illustrative.
Results are for engineering estimates; verify final designs against operating conditions and applicable standards.